The free behavior situation concerns the amount and temporal distribution of intake of a commodity in relation to the terms involved. For this purpose, rats live in chambers requiring them to work for all of their food or water by pressing on a bar; their intake is monitored regularly during the day and related to the amount of work required to obtain rewards of specified sizes. Daily intake is described by summary equations, and pattern of intake is related to a continuous-over-time model involving drive and effort constructs.